Scattering statistics of a negatively buoyant thermal plume

Abstract

High frequency acoustic scattering from inhomogeneous ocean environments is often assumed to be entirely coherent or incoherent. We hypothesize that the mean background stratification (which can also be interpreted as long-wavelength components of the inhomogeneity spectrum) cannot be ignored when estimating the total scattered power, leading to the sum of a coherent and incoherent component in the received pressure. In this work, we report laboratory measurements of scattering from a negatively buoyant thermal plume at 70, 120, and 200 kHz. Simple estimation of the coherent component was not possible because the sonar system rectified the signal. An alternative method to estimate the coherent component was to fit the pdf of the scattered field to a Rice distribution. It was found that at all frequencies, the pdf of the field scattered by plume boundary was lighter than Rayleigh and well fit by the Rice distribution. The coherent-to-incoherent power ratio of the field was highest for the lowest frequency. Scattering from the plume center was well fit by a Rayleigh distribution, indicating that the effect of background stratification is minimal away from the plume boundaries. Accompanying temperature and Doppler velocity measurements of the plume were used to support the acoustic measurements.High frequency acoustic scattering from inhomogeneous ocean environments is often assumed to be entirely coherent or incoherent. We hypothesize that the mean background stratification (which can also be interpreted as long-wavelength components of the inhomogeneity spectrum) cannot be ignored when estimating the total scattered power, leading to the sum of a coherent and incoherent component in the received pressure. In this work, we report laboratory measurements of scattering from a negatively buoyant thermal plume at 70, 120, and 200 kHz. Simple estimation of the coherent component was not possible because the sonar system rectified the signal. An alternative method to estimate the coherent component was to fit the pdf of the scattered field to a Rice distribution. It was found that at all frequencies, the pdf of the field scattered by plume boundary was lighter than Rayleigh and well fit by the Rice distribution. The coherent-to-incoherent power ratio of the field was highest for the lowest frequency....